1. Field of the Invention
The present invention relates to a resin joint for a resin fuel tank for connection to a piping tube or a connector, more specifically to a resin weld joint for being bonded to the resin fuel tank by heat-welding to construct a connecting portion between the resin fuel tank and the piping tube or the connector.
2. Description of the Related Art
A fuel tank equipped in a motor vehicle integrally has a joint that provides connection between the fuel tank and a tube, a connector or the like for introducing a fuel that is fed via a filler opening to the fuel tank.
Here, for example, for the tube introducing a fuel from the filler opening to the fuel tank, a tube made of rubber (rubber hose) has been used conventionally. In recent years, however, environmental regulations have been increasingly requiring to restrict a fuel from permeating out through a hose in view of environmental protection. This results in that, for a piping tube, employed is a rubber-resin composite hose of a composite of a rubber hose and a gas-barrier resin layer of fuel impermeability, a rubber tube formed of a fluoro-rubber of fuel impermeability or a resin tube made solely of resin.
For example, a connecting structure as shown in FIGS. 18A and 18B has been conventionally employed for connecting between such a tube and a fuel tank.
In FIGS. 18A and 18B, reference numeral 200 indicates a fuel tank made of resin, and reference numeral 202 indicates a weld joint also made of resin. The weld joint 202 is bonded integrally to the fuel tank 200 through application of heat-welding, or thermal-welding.
The weld joint 202 has a tubular portion 204 adapted for being inserted relatively into a tube, and an annular flange portion 206 projecting from an outer peripheral surface of the tubular portion 204.
Reference numeral 208 indicates a resin tube for introducing a fuel that is fed via a filler opening to the fuel tank 200. As shown in FIG. 18B, the resin tube 208 has a corrugated portion 210 that provides the resin tube 208 with flexibility.
In FIGS. 18B and 19, reference numeral 212 indicates a connector (quick connector). The resin tube 208 is connected to the weld joint 202 via the connector 212.
The connector 212 has a connector body 214 made of resin and a retainer 216 also made of resin.
The connector body 214 has a nipple portion 218 on one axial end thereof, and a socket like retainer holding portion 230 on the other axial end thereof. The retainer 216 is inserted resiliently in and held in the retainer holding portion 230.
The nipple portion 218 is press-fitted or force-fitted relatively in the resin tube 208 and secures the resin tube 208 thereon. The nipple portion 218 has a stop portion that is provided with a plurality of annular projecting portions 232 axially spaced on its outer peripheral surface. The stop portion has a saw-toothed cross-section. In an inner periphery of the nipple portion 218, a plurality of O-rings (seal rings) 234 are retained.
On the other hand, the socket like retainer holding portion 230 is formed with a circular arc window portion 236, and a partial-ring-shaped portion 238 of a corresponding circular arc shape.
The retainer 216 is entirely resiliently deformable in a radial direction. The retainer 216 has a circular arc groove 240 for resiliently fitting to the partial-ring-shaped portion 238 of the retainer holding portion 230, a tapered guide surface 242 for assisting axial insertion of the flange portion 206 of the weld joint 202 and assisting resilient diametrical expansion of the entire retainer 216, and circular arc fit-in slits 244 for fit-engaging the flange portion 206 therein.
In this connecting structure, an end portion of the resin tube 208 is forcibly press-fitted on the nipple portion 218 of the connector body 214, and is secured thereto.
During that state, the end portion of the resin tube 208 is deformed and diametrically expanded or flared by being press-fitted on the nipple portion 218 as shown in FIG. 18B, and radially tightens against the nipple portion 218 with a large tightening force.
This tightening force and a wedging function of the annular projecting portions 232 of the nipple portion 218 retain the end portion of the resin tube 208 onto the connector body 214 in a secured state.
Then, while the retainer 216 is mounted and held in the connector body 214, the connector 212 is fitted on the tubular portion 204 of the weld joint 202.
During that time, the retainer 216 held in the connector body 214 is resiliently deformed and diametrically expanded or flared by the flange portion 206. As soon as the flange portion 206 reaches the fit-in slits 244, the retainer 216 is resiliently deformed and diametrically contracted again to engage the flange portion 206 in the fit-in slits 244.
At the same time, a leading end of the tubular portion 204 with respect to the flange portion 206 fits in the O-rings 234 in an inner periphery of the connector body 214, and thereby an air tight seal is provided between the tubular portion 204 and the connector body 214.
On the other hand, aside from this, there is an idea that the resin tube 208 is connected to the weld joint 202 by putting or fitting the resin tube 208 immediately (directly) on the tubular portion 204 of the weld joint 202, without use of the above-mentioned connector 212.
Meanwhile, such weld joint adapted for connecting to a connector (quick connector) or connecting directly to a fuel piping tube is integrally bonded to the fuel tank by heat-welding as stated above. However, the following problem arises when a connecting portion for the tube is formed by bonding the weld joint integrally to a fuel tank through application of heat-welding.
Conventionally, for a material of an outer layer of the fuel tank, high density polyethylene (HDPE) resin has been used. So, the weld joint to be bonded integrally to the fuel tank is required to be weldable to the material of the outer layer.
Accordingly, there is an idea that the entire weld joint including a tubular portion is made of the same material of HDPE resin. HDPE resin is excellent in weldability to the fuel tank, but insufficient in fuel permeation resistance (fuel impermeability). This causes a problem that a fuel permeates out through this portion.
Patent Document 1 stated below discloses a weld joint for the purpose of solving the problem relative to fuel impermeability. According to Patent Document 1, the weld joint is constructed by radially laying an outer layer having weldability to a fuel tank on an inner layer made of resin having fuel impermeability (gas-barrier property).
FIG. 20 shows an illustrative example of such weld joint.
In FIG. 20, reference numeral 246 indicates a resin fuel tank constructed by laying an outer layer 246-1 made of HDPE resin, a gas-barrier layer 246-2 made of ethylene-vinyl alcohol copolymer (EVOH) resin of superior fuel impermeability and an inner layer 246-3 made of HDPE resin, on one another.
Reference numeral 248 indicates a resin weld joint that is welded integrally to the fuel tank 246. The weld joint 248 has a tubular portion 252 serving as a connecting portion (a plug-in portion) to a tube 258, and a weld portion 250 at a base end portion thereof. The weld joint 248 is bonded to the fuel tank 246 at the weld portion 250 by heat-welding.
The tubular portion 252 has an outer layer 254 and an inner layer 256. The outer layer 254 and the inner layer 256 are made of different resin materials. Specifically, the outer layer 254 is made of the same material as the weld portion 250, and the inner layer 256 is made of gas-barrier material such as polyamide (PA) resin that is more excellent in fuel impermeability than the outer layer 254.
Meantime, reference numeral 260 indicates a hose band for securing the tube 258 on the tubular portion 252 in a fit-on state by clamping the tube 258.
In the weld joint 248 of this construction, the outer layer 254 of the tubular portion 252 and the weld portion 250 are made of HDPE resin of the same material as the outer-layer 246-1 of the fuel tank 246. As stated above, HDPE resin has good weldability to the fuel tank 246. But, HDPE resin does not have sufficient fuel impermeability, in the weld joint 248 as shown in FIG. 20, the inner layer 256 made of the gas-barrier material is provided in the tubular portion 252. Therefore, fuel impermeability is ensured for the tubular portion 252. However, the weld portion 250 of HDPE resin is left, so to speak, in exposed condition.
So, a weld joint 262 as shown in FIG. 21 is proposed in the previous patent application (Patent Document 2 as stated below). The entire weld joint 262, specifically the entire weld joint 262 including a tubular portion 264 and a weld portion 266 to be welded to a fuel tank 246 is made of a resin alloy material obtained by alloying EVOH with a modified HDPE (not with HDPE), or a resin alloy material obtained by alloying EVOH with the modified HDPE and HDPE. The modified HDPE is obtained by introducing a functional group of high affinity for a hydroxyl group of EVOH into HDPE.
EVOH has been known as a material having excellent gas-barrier property or fuel-barrier property since a long time ago. The resin alloy material obtained by alloying such EVOH with the above-mentioned modified HDPE (not with HDPE) or the resin alloy material obtained by alloying such EVOH with the above-mentioned modified HDPE and HDPE has excellent weldability to the fuel tank 246 derived from HDPE or the modified HDPE contained herein, and also has very excellent fuel impermeability (gas-barrier property) derived from EVOH. Therefore, in the construction as shown in FIG. 21, the tubular portion 264 and the weld portion 266 can be provided with good fuel impermeability, and at the same time, the weld portion 266 can be expected to have high weldability to the fuel tank 246. Further, in the weld joint 262, because the entire weld joint 262 including the tubular portion 264 and the weld portion 266 is made of the same single material, the number of the steps required for production or formation can be reduced and thereby the cost for the weld joint 262 can be reduced. Further, similarly to EVOH, PA is also a material having excellent gas-barrier property or fuel-barrier property. So, the weld joint 262 may be made of a resin alloy material obtained by alloying PA with a modified HDPE (not with HDPE), or a resin alloy material obtained by alloying PA with the modified HDPE and HDPE. The modified HDPE is obtained by introducing a functional group of high affinity for an amine group of PA into HDPE. A similar advantage can be expected also for this alloy material.
However, as a result of a test for weld performance of such a weld joint 262 to the fuel tank 246, it is found that weld strength of the weld joint 262 to the fuel tank 246 actually varies, depending on various welding conditions, for example, such as fusing temperature, fusing time, fusion margin (fused thickness) of a resin of the weld joint 262 or the fuel tank 246, weld pressure, or weld time during welding operation, as a result, sufficient weld strength cannot always be obtained consistently.
In the weld joint 262 made of the above resin alloy material shown in FIG. 21, the weld portion 266 has higher weldability compared to a weld joint made solely of EVOH, but does not have so high weldability as a weld portion made of HDPE resin has. Due to this reason, when the weld joint 262 is welded to the resin fuel tank 246 at the weld portion 266, the weld portion 266 is not welded sometimes sufficiently. That is, there exist variations in welding result, such as excessive welding strength or insufficient welding strength, depending on welding conditions during welding operation. Similar problems are assumed also when fuel impermeable resins other than EVOH or PA are used in a weld joint.
[Patent Document 1] JP-A-2002-254938
[Patent Document 2] JP-A-2006-143172
Under the circumstances described above, it is an object of the present invention to provide a weld joint capable of being bonded to a resin fuel tank with consistent and sufficient welding strength, in the case at least a weld portion of the weld joint is made of a resin alloy material obtained by alloying a barrier resin of fuel impermeability such as EVOH or PA with modified HDPE, or with the modified HDPE and HDPE.